Casing structure of compressed wood

ABSTRACT

A casing structure of compressed wood that holds a predetermined object between a plurality of compressed wood pieces, wherein each of the compressed wood pieces has a main surface portion and side surface portions formed integrally around entire peripheral edges of the main surface portion and non-parallel with the main surface portion, and wood fiber directions in the main surface portions of the compressed wood pieces are substantially symmetrical with respect to an opposing surface between the compressed wood pieces.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of PCT/JP2005/002679 filed onFeb. 15, 2005, which claims priority to Japanese Patent Application No.2004-059271, filed on Mar. 3, 2004.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The present invention relates to a casing structure using compressedwood.

2) Description of the Related Art

Conventionally, light metals (for example, aluminum, stainless steel,titanium, and magnesium) and synthetic resins (for example,acrylonitrile-butadiene-styrene (ABS), polycarbonate, and acrylicresins) are used as a material of a casing for electronic device (forexample, a digital camera, a mobile phone, and an IC recorder). A casingformed of the above materials has a relatively smallexpansion/contraction rate when it absorbs and discharges moisture, andthe expansion/contraction rate thereof is approximately the same in alldirections since such a casing is isotropic. However, when the casing isevaluated as an exterior packaging member, the casing is disadvantageousin that it has no individual characteristics because it has almost noindividual difference. Further its design property is deterioratedbecause scratches and discoloring occur over a long term use.

To solve the above problems, the inventor has conceived of forming acasing with wood. The use of wood is advantageous in that it can providean appropriate individual difference because of grains that differ fromone another and further in that the change of surface color over a longterm use serves to enhance a design property. However, when wood is usedas the casing material as described above, the rigidity of the casingmay not be good enough compared with the casings of the light metal andthe synthetic resin. Although the thickness of the casing may beincreased to compensate the deterioration of the rigidity, this is notsuitable for a casing for electronic device in which downsizing isparticularly required.

One conventionally known method to improve the strength of wood materialis compression processing. According to the method, wood is softenedthrough water absorption and compressed while being fixed in apredetermined shape, and sliced in a direction of compression to be aplate-like primary fixed product. Subsequently, the primary fixedproduct is shaped into a product with a predetermined three-dimensionalshape while being heated and made to absorb water, and fixed in thepredetermined three-dimensional shape to be a final product (see, forexample, Japanese Patent No. 3078452). According to another knownmethod, softened wood is compressed and fixed (see, for example,Japanese Patent Application Laid-Open No. 11-77619). Accordingly, whenthese methods are used, the strength of wood might be enhanced withoutthe increase in wall thickness.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least solve the problemsin the conventional technology.

A casing structure of compressed wood that holds a predetermined objectbetween a plurality of compressed wood pieces, according to one aspectof the present invention, wherein each of the compressed wood pieces hasa main surface portion and side surface portions formed integrallyaround entire peripheral edges of the main surface portion andnon-parallel with the main surface portion, and wood fiber directions inthe main surface portions of the compressed wood pieces aresubstantially symmetrical with respect to an opposing surface betweenthe compressed wood pieces.

A casing structure of compressed wood that holds a predetermined objectbetween a plurality of compressed wood pieces, according to anotheraspect of the present invention, wherein each of the compressed woodpieces has a main surface portion formed in a substantially square shapeand side surface portions formed integrally around four peripheral edgesof the main surface portion and non-parallel with the main surfaceportion, and wood fiber directions in the main surface portions of thepair of compressed wood pieces are substantially symmetrical withrespect to an opposing surface between the pair of compressed woodpieces.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electronic device using a casingstructure of compressed wood according to a first embodiment of thepresent invention;

FIG. 2 is an exploded perspective view of the electronic device shown inFIG. 1;

FIG. 3 is a sectional view of the electronic device taken along a lineA-A indicated by an arrow shown in FIG. 1;

FIG. 4 is a sectional view of the electronic device 1 in anexpanded/contracted state taken along the line A-A shown in FIG. 1;

FIG. 5 is an enlarged sectional view of a joint portion shown in FIG. 3;

FIG. 6 is a perspective view of a joint structure;

FIG. 7 is a perspective view of shaping of wood piece according to thefirst embodiment;

FIG. 8 is a plan view of shaping of the wood piece according to thefirst embodiment;

FIG. 9 is a perspective view of a compression process of the wood pieceaccording to the first embodiment;

FIG. 10 is a longitudinal sectional view that sequentially depictsrespective compression processes of the wood piece according to thefirst embodiment;

FIG. 11 is a longitudinal sectional view that sequentially depictsrespective compression processes of the wood piece according to thefirst embodiment;

FIG. 12 is a longitudinal sectional view that sequentially depictsrespective compression processes of the wood piece according to thefirst embodiment;

FIG. 13 is a perspective view of an electronic device using a casingstructure of compressed wood according to a second embodiment of thepresent invention;

FIG. 14 is an exploded perspective view of the electronic device shownin FIG. 13;

FIG. 15 is a perspective view of shaping of wood piece according to thesecond embodiment;

FIG. 16 is a perspective view of an electronic device using a casingstructure of compressed wood according to a third embodiment of thepresent invention when the electronic device is viewed from a rearsurface direction;

FIG. 17 is an exploded perspective view of the electronic device when abattery cover is removed;

FIG. 18 is a perspective view of an electronic device using a casingstructure of compressed wood according to a fourth embodiment of thepresent invention when the electronic device is viewed from a rearsurface direction; and

FIG. 19 is an exploded perspective view of the electronic device when abattery cover is removed.

DETAILED DESCRIPTION

Exemplary embodiments of a forming apparatus relating to the presentinvention will be explained in detail below with reference to theaccompanying drawings.

The first embodiment of the casing structure of compressed wood is firstexplained. General features of the casing structure according to thefirst embodiment reside in that: (1) each of a plurality (a pair) ofcompressed wood pieces has a main surface portion, which is formed in asubstantially square shape, and side surface portions, which are formedintegrally to four peripheral edges of the main surface portion andnon-parallel therewith, wherein the wood fiber directions in the mainsurface portions of compressed wood pieces are substantially symmetricalwith respect to an opposing surface between the compressed wood pieces;and that (2) the wood fiber direction in the main surface portion issubstantially parallel with the longitudinal direction of the mainsurface portion.

FIG. 1 is a perspective view of an electronic device using the casingstructure of the compressed wood according to the first embodiment. InFIG. 1, the electronic device 1 is a digital camera including a casing10 and an electronic unit 20. The casing 10 accommodates the electronicunit 20 as an object to be held in a holding space formed therein. Thecasing 10 holds the electronic unit 20 integrally therein as well asprotects the electronic unit 20 from the outside of the casing 10. Thecasing 10 also serves as an exterior packaging member of the electronicdevice 1 through exposing the outer surface thereof to the outside.

The electronic unit 20 causes the electronic device 1 to implementnecessary electronic functions and includes, for example, an imaginglens 21, a shutter button 22, a liquid crystal monitor, an image pickupdevice, a drive circuit for various devices, and terminals to beconnected to external equipment. FIG. 1 depicts only the imaging lens 21and the shutter button 22 among the components of the electronic unit20.

As shown by arrows in FIG. 1, in the following explanation, a directionX along the long side of the electronic device 1 is called alongitudinal direction, a direction Y along a short side of theelectronic device 1 and orthogonal to the longitudinal direction of theelectronic device 1 is called a lateral direction, and a direction Zorthogonal to the longitudinal direction and the lateral direction iscalled a thickness direction. A dimension of the electronic device inthe longitudinal direction is called a long size, a dimension thereof inthe lateral direction is called a short size, and a dimension thereof inthe thickness direction is called a thickness. The wood fiber directionis a direction in which a wood grows in a wood growing process(direction from a root of the wood to an extreme end thereof, that is, adirection which is substantially parallel with a flat grain surface anda straight grain surface, and substantially orthogonal to an end grainsurface. Grain is generally a visible pattern formed by the gradation ofwood fiber density. However, the term “grains” used herein indicates adistribution of wood fiber densities irrespective of the visibility.

A specific structure of the casing 10 is explained next. FIG. 2 is anexploded perspective view of the electronic device shown in FIG. 1, FIG.3 is a sectional view of the electronic device shown in FIG. 1 takenalong a line A-A indicated by an arrow in FIG. 1, and FIG. 4 is asectional view of the electronic device 1 shown in FIG. 1 in anexpanded/contracted state taken along the line A-A indicated by thearrow in FIG. 1. The electronic unit is not shown in FIG. 2. As shown inthe respective drawings, the casing 10 is composed of a plurality ofcompressed wood pieces combined with each other. In the firstembodiment, the casing 10 is a combination of a pair of compressed woodpieces, that is, a front panel 11 and a rear panel 12.

The front panel 11 and the rear panel 12 are formed and processed into ashape corresponding to the shape of the object to be held therein. Inparticular, the front panel 11 has a lens hole 13 for exposing theimaging lens 21 to the outside, and the rear panel 12 has a monitor hole14 for exposing the liquid crystal monitor. Further, the front panel 11and the rear panel 12 have a shutter hole 15 for exposing the shutterbutton 22 and a terminal hole 16 for allowing the connection terminal tobe connected to the external equipment, respectively.

The front panel 11 has a flat main surface portion 11 a and side surfaceportions 11 b to 11 e formed around the peripheral edges of the mainsurface portion 11 a, and the rear panel 12 has a flat main surfaceportion 12 a and side surface portions 12 b to 12 e formed around theperipheral edges of the main surface portion 12 a. The side surfaceportions 11 b to 11 e and 12 b to 12 e are formed around all theperipheral edges of the main surface portions 11 a and 12 a,respectively. Since the main surface portions 11 a and 12 a are formedin a square shape and have the peripheral edges in four directions, theside surface portions 11 b to 11 e and 12 b to 12 e are formed aroundthe four peripheral edges of the main surface portions 11 a and 12 a,respectively.

The side surface portions 11 b to 11 e and 12 b to 12 e are formednon-parallel with the main surface portions 11 a and 12 a, respectively.Specifically, the side surface portions 11 b to 11 e of the front panel11 are arranged to rise toward the rear panel 12, and the side surfaceportions 12 b to 12 e of the rear panel 12 are arranged to rise towardthe front panel 11. The angles between the main surface portions 11 aand the side surface portions 11 b to 11 e and the angles between themain surface portions 12 a and the side surface portions 12 b to 12 ecan be set to arbitrary angles other than zero degree as long as theyare non-parallel with each other. In the first embodiment, the sidesurface portions 11 b to 11 e and 12 b to 12 e are substantiallyorthogonal to the main surface portions 11 a and 12 a, respectively.

In particular, the side surface portions 11 b to 11 e and 12 b to 12 eare formed integrally with the main surface portions 11 a and 12 a,respectively. In other words, the side surface portions 11 b to 11 e and12 b to 12 e are formed while continuously bending the wood fibers whichare contained in the main surface portions 11 a and 12 a, in anon-parallel state therewith, respectively, by the pressure applied by apress or the like so that the wood fibers are not made discontinuous. Inthis regard, the casing 10 is essentially different from a conventionalwooden box, a canoe which is formed by scraping, or the like.

The wood fiber directions of the front and rear panels 11 and 12 areexplained next. Assume that an imaginary opposing surface P existsbetween the front panel 11 and the rear panel 12 as shown in FIGS. 3 and4. Then, the respective wood fiber directions of the main surfaceportions 11 a and 12 a, and the side surface portions 11 b to 11 e and12 b to 12 e are substantially symmetrical with respect to the opposingsurface P. Specifically, the respective wood fibers of the main surfaceportions 11 a and 12 a and the side surface portions 11 b to 11 e and 12b to 12 e are oriented along the longitudinal direction.

In other words, the surfaces which confront with each other, that is,the main surface portions 11 a and 12 a, the side surface portions 11 band 12 b, the side surface portions 11 c and 12 c, the side surfaceportions 11 d and 12 d, and the side surface portions 11 e and 12 e, areformed to have the wood fibers along substantially the same direction(although the sections of the front and rear panels 11 and 12 are shownby hatching in FIGS. 3 and 4, they do not represent either actual woodfibers or grains, and this is also applied to FIG. 5 described later). Amethod of forming the front and rear panels 11 and 12 as described aboveis explained later.

The state of the casing 10 at expansion and contraction is explainednext. As shown in FIG. 3, the long size Lf of the front panel 11 isapproximately the same as the long size Lr of the rear panel 12. It isassumed here that the front and rear panels 11 and 12 expand or contractthrough moisture absorption or discharge. As shown in FIG. 4, here, anamount of expansion/contraction of the front panel 11 in thelongitudinal direction at the expansion/contraction is indicated by ΔLf,and an amount of expansion/contraction of the rear panel 12 in thelongitudinal direction at the expansion/contraction is indicated by ΔLr.

Here, since the compressed wood piece has anisotropy, theexpansion/contraction rates are different among respective directions.More specifically, the expansion/contraction rates differ depending onthe wood fiber directions. As described above, the wood fiber directionsof the front and rear panels 11 and 12 are substantially symmetricalwith respect to the opposing surface P therebetween. Accordingly, theamount of expansion/contraction ΔLf of the front panel 11 in thelongitudinal direction is equal to the amount of expansion/contractionΔLr of the rear panel 12 in the longitudinal direction. Therefore, afterthe front and rear panels 11 and 12 expand/contract, the long sizeLf+ΔLf of the front panel 11 is equal to the long size Lr+ΔLr of therear panel 12 as shown in FIG. 4.

The same relations also hold for the lateral direction. Before the frontand rear panels 11 and 12 expand/contract, the short size of the frontpanel 11 is equal to the short size of the rear panel 12. After thefront and rear panels 11 and 12 expand/contract, the short size of thefront panel 11 is equal to the short size of the rear panel 12.

Accordingly, even if the front and rear panels 11 and 12expand/contract, they can be kept in of the same length, and thus therelative positional relation therebetween can be maintained. As aresult, the relative positional displacement between the front and rearpanels 11 and 12 can be prevented, the design property thereof can bemaintained, generation of gaps in the casing 10 can be prevented, andfurther generation of cracks and the like in joint portions can beprevented as the application of excessive stress thereto through theexpansion/contraction can be avoided. Further, since generation of gapsin the casing 10 can be prevented, a necessary creepage distance can besecured even if a high voltage unit is included in the electronic unit20.

In particular, in the first embodiment, the wood fiber directions of themain surface portions 11 a and 12 a are substantially parallel with thelongitudinal direction thereof, respectively, as shown in FIGS. 1 and 2.In general, it is known that the expansion and contraction of a wood isminimum in the wood fiber direction. Accordingly, when the wood fiberdirection is substantially parallel with the longitudinal direction asin the first embodiment, the wood fiber direction in which the expansionor contraction of the main surface portions 11 a and 12 a is minimum canbe in coincidence with the longitudinal direction, which is mostaffected by the expansion and contraction, of the main surface portions11 a and 12 a, whereby the mutual positional displacement and the likebetween the front and rear panels 11 and 12 can be more effectivelyprevented.

A joint structure of the front panel 11 and the rear panel 12 isexplained next. FIG. 5 is an enlarged sectional view of a joint portionshown in FIG. 3, and FIG. 6 is a perspective view of the jointstructure. As shown in FIGS. 5 and 6, a tenon portion 12 f is formedaround the entire periphery of the surface of the rear panel 12 facingthe front panel 11. On the other hand, a mortise portion 11 f, which hasa shape corresponding to the tenon portion 12 f, is formed around theentire periphery of the surface of the front panel 11 facing the rearpanel 12. The front panel 11 is joined to the rear panel 12 through theinsertion of the tenon portion 12 f into the mortise portion 11 f. Therelative positional relation between the front panel 11 and the rearpanel 12 is maintained as described above even if such a strong jointstructure is employed, whereby generation of cracks and the like can beprevented in the joint portion. Note that any joint structure may beemployed between the front and rear panels 11 and 12, and a water-proofstructure using a rubber packing may be employed.

A method of forming the front and rear panels 11 and 12 is explainednext. Since the front and rear panels 11 and 12 can be formed in thesame manner a method of forming the front panel 11 is explained below.FIG. 7 is a perspective view of shaping of a wood piece according to thefirst embodiment. As shown in FIG. 7, first, a wood piece 31 is shapedfrom an uncompressed raw wood 30. The wood piece 31 is shaped in such amanner that the longitudinal direction thereof is in coincidence withthe wood fiber direction Lw of the raw wood 30. The wood piece 31includes the main surface portion 11 a and the side surface portions 11b to 11 e of the front panel 11 integrally, and the main surface portion11 a is connected to the side surface portions 11 b to 11 e throughsmooth curved surfaces. In FIG. 7, the grains of the raw wood 30 aredenoted by a reference numeral 32.

FIG. 8 is a plan view of shaping of the wood piece according to thefirst embodiment. As shown in FIG. 8, the wood piece 31 which is shapedfrom the raw wood 30 can be a wood piece 31-1, a wood piece 31-2, and awood piece 31-3 that differ in the positions with respect to the grains32. In the present embodiment, the wood piece 31 is cut as the woodpiece 31-1 so that the wood fiber direction is substantially parallelwith the longitudinal direction of the main surface portion 11 a.However, the position in which the wood piece 31 is cut may bearbitrarily determined as far as the advantageous effect of theembodiment particularly described herein can be achieved with respect tothe wood fiber direction.

FIG. 9 is a perspective view of a compression process of the wood pieceaccording to the first embodiment and FIGS. 10 to 12 are longitudinalsectional views that sequentially depict respective compressionprocesses of the wood piece according to the first embodiment To brieflyexplain, the front panel 11, which includes the main surface portion 11a and the side surface portions 11 b to 11 e integrally therewith, isformed through the pressing of the wood piece 31 between a lower moldframe 40 and an upper mold frame 41 as shown in FIG. 9.

A shape of the wood piece 31 is explained first. The wood piece 31 islumbered in a shape to which the volume of the wood piece 31 to bereduced by compression is previously added. Specifically, as shown inFIG. 10, the main surface portion 11 a is shaped so as to have athickness W1 to which the volume thereof reduced by compression ispreviously added, and the side surface portions 11 b to 11 e are shapedso as to have a thickness W2 and a height T1 to which the volume thereofreduced by compression is previously added, respectively. The frontpanel 11 is shaped to have a width H1 as a whole. The thickness W1 ofthe main surface portion is made larger than the thickness W2 of theside surface portions.

The relation between the shape of the wood piece 31 and the shapes ofthe lower and upper mold frames 40 and 41 is explained next. As shown inFIGS. 10 to 12, the relation between the radius of curvature of anoutside curved surface RO of the wood piece 31 and the radius ofcurvature of a curved surface RA of a concave portion 40 a of the lowermold frame 40 opposing the curved surface RO is shown by RO>RA. On theother hand, the relation between the radius of curvature of a curvedsurface RI of the wood piece 31 and the radius of curvature of a curvedsurface RB of a convex portion 41 a of the upper mold frame 41 is shownby RI>RB. Further, as shown in FIG. 11, a space which is formed betweenthe lower mold frame 40 and the upper mold frame 41 when they arecombined with each other, has a shape corresponding to the shape of thefront panel 11 after the compression of the wood piece 31.

A specific forming method is explained next. First, as shown in FIG. 10,the wood piece 31 is placed between the lower mold frame 40 and theupper mold frame 41. At the same time, the wood piece 31 is placed in awater vapor atmosphere of high temperature and high pressure for apredetermined time so that it is softened by excessive absorption ofmoisture. Next, as shown in FIG. 11, the upper mold frame 41 is fittedinto the lower mold frame 40 to compress the wood piece 31. Then, thewood piece 31 is left as it is for a predetermined period of time in astate that a compression force is applied thereto. Finally, the woodpiece 31 is released from the water vapor atmosphere of high temperatureand high pressure, and the thus formed front panel 11 is taken out byseparating the upper mold frame 41 from the lower mold frame 40 as shownin FIG. 12. The taken-out front panel 11 has been compressed so that themain surface portion 11 a and the side surface portions 11 b to 11 ehave substantially uniform thicknesses W1′ and W2′, respectively, andthe side surface portions 11 b to 11 e have a height T1′. Further,curved portions 1 c are compressed obliquely. The front panel 11 iscompressed to have a width H1′ as a whole. The front panel 11, which isformed by compression as described above, is provided with a highstrength in its entirety because the fiber density thereof is increased.

The second embodiment of the casing structure of the compressed wood isexplained next. A main feature of the second embodiment is such that thegrains of the main surface portions thereof are substantiallysymmetrical with respect to an opposing surface between compressed woodpieces, in addition to the feature of the first embodiment Note that astructure and a method of the second embodiment are the same as those ofthe first embodiment described above unless explained otherwise, andlike reference numerals designate like components as those of the firstembodiment.

FIG. 13 is a perspective view of an electronic device using the casingstructure of the compressed wood according to the second embodiment, andFIG. 14 is an exploded perspective view of the electronic device shownin FIG. 13 (electronic unit is not shown in FIG. 14). As shown in thedrawings, a casing 60 is composed of a pair of compressed wood pieces,that is, a front panel 61 and a rear panel 62 combined with each other.

The front panel 61 has a flat main surface portion 61 a and side surfaceportions 61 b to 61 e integrally formed around the four peripheral edgesof the main surface portion 61 a non-parallel therewith, and the rearpanel 62 has a flat main surface portion 62 a and side surface portions62 b to 62 e integrally formed around the four peripheral edges of themain surface portion 62 a non-parallel therewith. The wood fiberdirections of the main surface portions 61 a and 62 a and the sidesurface portions 61 b to 61 e and 62 b to 62 e are substantiallysymmetrical with respect to an opposing surface P (not shown) betweenthe front and rear panels 61 and 62. Accordingly, even if the front andrear panels 61 and 62 expand or contract, they can be kept in of thesame length, whereby the relative positional relation thereof ismaintained.

In particular, in the second embodiment, the front panel 61 and the rearpanel 62 are formed so that the grains thereof are symmetrical withrespect to the opposing surface P therebetween. That is, thedistribution of wood fiber density in the front panel 61 issubstantially the same as that in the rear panel 62 across the opposingsurface R This relation holds almost commonly for all the distributionsof wood fiber density in the side surface portions 61 b to 61 e and 62 bto 62 e. Accordingly, even if the front and rear panels 61 and 62expand/contract, the relative positional relation thereof can be moreeffectively maintained. Further, since the grains are in coincidencewith each other, a visually continuous casing structure is provided bythe front and rear panels 61 and 62, therefore a design property can befurther enhanced.

A method of forming the front and rear panels 61 and 62 is explainednext. FIG. 15 is a perspective view of shaping of wood pieces accordingto the second embodiment. As shown in FIG. 15, wood pieces 31 and 31′for forming the front and rear panels 61 and 62 are shaped from the rawwood 30 at positions symmetrical with respect to the center C thereof.The front and rear panels 61 and 62 can be formed through thecompression of the wood pieces 31 and 31′ in a water vapor atmosphere ofhigh temperature and high pressure using a lower mold frame 40 and anupper mold frame 41 like the first embodiment. However, the front andrear panels 61 and 62 may be formed by any arbitrary method as long asthey are formed symmetrical with respect to the opposing surface Ptherebetween as to also the grains thereof.

The third embodiment of the casing structure of the compressed wood isexplained next. A main feature of the third embodiment is such that apart of a compressed wood piece is formed as a detachable unit that isdetachably mounted on the compressed wood piece, and the wood fiberdirection of the detachable unit is substantially in coincidence withthat of the compressed wood piece on which the detachable unit ismounted, in addition to the features of the first and the secondembodiments. Note that a structure and a method of the third embodimentare the same as those of the second embodiment described above unlessexplained otherwise, and like reference numerals designate likecomponents as those of the second embodiment.

FIG. 16 is a perspective view from the back of an electronic deviceusing the casing structure of the compressed wood according to the thirdembodiment, and FIG. 17 is an exploded perspective view of theelectronic device when a battery cover is removed. As shown in thedrawings, a casing 70 is composed of a pair of compressed wood pieces,that is, a front panel 71 and a rear panel 72 combined with each other.

The front panel 71 has a flat main surface portion 71 a and side surfaceportions 71 b to 71 e integrally formed around the four peripheral edgesof the main surface portion 71 a non-parallel therewith, and the rearpanel 72 has a flat main surface portion 72 a and side surface portions72 b to 72 e integrally formed around the four peripheral edges of themain surface portion 72 a non-parallel therewith. The wood fiberdirections of the main surface portions 71 a and 72 a and the sidesurface portions 71 b to 71 e and 72 b to 72 e are substantiallysymmetrical with respect to an opposing surface P (not shown) betweenthe front and rear panels 71 and 72. Accordingly, even if the front andrear panels 71 and 72 expand or contract, they can be kept in of thesame length, thereby maintaining the relative positional relationthereof.

The rear panel 72 is provided with a battery cover 90 as a detachableunit which is detachably mounted thereon. A part of the main surfaceportion 72 a of the rear panel 72 is cut in square to form the batterycover 90. The battery cover 90 is detachable from the main surfaceportion 72 a by locking/unlocking of locking portions 91 formed on bothsides of the battery cover 90 to/from the side edges of an opening 72 fof the main surface portion 72 a. A known structure can be employed as aspecific locking structure. A battery 92 can be replaced by detachingthe battery cover 90 from the main surface portion 72 a as shown in FIG.17.

The wood fiber direction of the battery cover 90 is substantially incoincidence with that of the main surface portion 72 a on which thebattery cover 90 is detachably mounted. In other words, as shown by anarrow in FIG. 16, the battery cover 90 is formed and disposed so thatthe wood fiber direction of the battery cover 90 is substantially incoincidence with the longitudinal direction of the main surface portion72 a. Accordingly, even if the main surface portion 72 a expands orcontracts, the battery cover 90 expands or contracts at the sameexpansion/contraction rate as that of the main surface portion 72 a,whereby the relative positional relation between the main surfaceportion 72 a and the battery cover 90 is maintained.

The fourth embodiment of the casing structure of the compressed wood isexplained next. A main feature of the fourth embodiment is such that thewood fiber direction of a detachable unit is substantially incoincidence with that of the compressed wood piece on which thedetachable unit is mounted like the third embodiment. Note that astructure and a method of the fourth embodiment are the same as those ofthe third embodiment described above unless explained otherwise, andlike reference numerals designate like components as those of the thirdembodiment.

FIG. 18 is a perspective view of an electronic device using the casingstructure of the compressed wood according to the fourth embodiment asviewed from the rear surface direction, and FIG. 19 is an explodedperspective view of the electronic device when the battery cover isremoved. As shown in the drawings, a casing 80 is composed of a pair ofcompressed wood pieces, that is, a front panel 81 and a rear panel 82combined with each other.

The front panel 81 has a flat main surface portion 81 a and side surfaceportions 81 b to 81 e integrally formed around the four peripheral edgesof the main surface portion 81 a non-parallel therewith, and the rearpanel 82 has a flat main surface portion 82 a and side surface portions82 b to 82 e integrally formed around the four peripheral edges of themain surface portion 82 a non-parallel therewith. The wood fiberdirections of the main surface portions 81 a and 82 a and the sidesurface portions 81 b to 81 e and 82 b to 82 e are substantiallysymmetrical with respect to an opposing surface P (not shown) betweenthe front and rear panels 81 and 82. Accordingly, even if the front andrear panels 81 and 82 expand or contract, they can be kept in of thesame length, whereby the relative positional relation thereof ismaintained.

The rear panel 82 is provided with a battery cover 100 as a detachableunit detachably mounted thereon. One end of the rear panel 82 is dividedto form the battery cover 100. In particular, the battery cover 100 iscomposed of parts of the main surface portion 82 a and the side surfaceportions 82 b and 82 d of the rear panel 82 and the entire side surfaceportion 82 c thereof.

A tenon portion 101 is formed on the surface of the front panel 81facing the battery cover 100, and a mortise portion 102 having a shapecorresponding to that of the tenon portion 101 is formed on the surfaceof the battery cover 100 facing the front panel 81. The battery cover100 can be mounted as shown in FIG. 18 by sliding it while inserting thetenon portion 101 into the mortise portion 102. A known structure can beemployed as a specific mounting structure. A battery 103 can be replacedby detaching the battery cover 100 from the rear panel 82 as shown inFIG. 19.

The wood fiber direction of the battery cover 100 is substantially incoincidence with that of the rear panel 82. That is, the battery cover100 is formed and disposed so that the wood fiber direction thereof issubstantially in coincidence with the longitudinal direction of the rearpanel 82. Accordingly, even if the rear panel 82 expands or contracts,the battery cover 100 expands or contracts at substantially the sameexpansion/contraction rate as that of the rear panel 82, whereby therelative positional relation between the rear panel 82 and the batterycover 100 is maintained.

Finally, a possibility of modifying the above embodiments is explained.The specific structures and methods of the above embodiments accordingto the present invention described above can be arbitrarily modified andimproved within the range of the technical spirits of inventive conceptdefined in the appended claims. Further, the problem to be solved by thepresent invention and the effect achieved by the present invention arenot limited to those described above, and it is possible to solve aproblem that is not described above and to achieve an effect that is notdescribed above, and it is also possible to solve only a part of theproblem described and to achieve only a part of the effect describedabove.

For example, the electronic device is not limited to the digital cameradescribed above and may be arranged as a mobile phone, an IC recorder, apersonal digital assistant (PDA), a portable television, a portableradio, a remote controller for various home electric appliances. In theabove explanation, the terms such as “parallel” and “orthogonal” areused to describe the structure. These descriptions, however, do not meanstrictly parallel and orthogonal, and the structures described as suchmay be non-parallel and non-orthogonal to an extent that would allow thestructures to exert the advantageous function of the invention. Inparticular, since wood, which is a natural material, is used in thestructures, at least an error which may occur in an ordinary processingof wood is permitted. Further, the sizes and the rates of the variousportions explained in the particular embodiments are only examples, andthe respective portions may be formed to have any arbitrary sizes andrates different from those described above.

The casing structure may be composed of any arbitrary number ofcompressed wood pieces, and it may be composed of, for example, two tofour compressed wood pieces combined together. Further, the compressedwood pieces may be formed in any arbitrary shape, and the casingcomposed of a combination of the compressed wood pieces may be formed inany arbitrary shape such as a cylindrical shape or an egg shape. Themethod of forming the compressed wood piece is not limited to. themethod explained above, and, for example, compression and forming ofupwardly curved side surface portions may be simultaneously performed ona wood piece which is cut off in a flat shape, through the applicationof pressure thereon between the mold frames. Alternatively, the wood maybe compressed in a direction other than the direction described above ormay be compressed from a plurality of directions.

Further, the casing may be formed by indirectly combining the compressedwood pieces, except by directly combining them. For example, a pluralityof the compressed wood pieces may be combined with each other with othermetal or resin member fitted therebetween. Further, the detachable unitdetachably mounted on the compressed wood piece is not limited to thebattery cover as described in the third and the fourth embodiments, andit may be arranged as a detachable unit for achieving an arbitraryfunction.

When a casing is composed of compressed wood, a new problem arises inaddition to the deterioration of rigidity. Wood has a largeexpansion/contraction rate when it absorbs or discharges moisturealthough it has a very small coefficient of thermal expansion, and itsmaximum expansion and contraction is about 10%. Further, since the woodhas anisotropy, it may not expand and contract uniformly in alldirections. Further, the expansion/contraction rate of compressed woodmay become larger than that of non-compressed wood. Most casings forelectronic device are composed of a plurality of exterior packagingmembers joined with each other. Accordingly, when the respectiveexterior packaging members greatly expand or contract by absorbing ordischarging moisture, the relative positions of exterior packagingmembers may shift to deteriorate the design property, or to create gapsin the casing. Further an excessive stress applied on a joint portiondue to the expansion or contraction may create cracks in the jointportion. When an electronic device includes a high voltage unit (forexample, an electronic flash unit in a digital camera), it may bedifficult to insulate the high voltage unit from the exterior of thedevice. In particular, when the gaps are generated in the casing, acreepage distance for insulation (shortest distance along a surface ofan insulator between two conductive components) is shortened between thehigh voltage unit and the exterior of the device, which is notpreferable because it may make it difficult to secure a predeterminedcreepage distance for insulation regulated by a safety standard.

In the casing structure of the compressed wood according to theembodiments, even if a plurality of compressed wood pieces expands orcontracts, they can be kept to the same length because the wood fiberdirections in the main surface portions of the compressed wood piecesare substantially symmetrical with respect to the opposing surfacebetween the compressed wood pieces. Accordingly, the relative positionalrelation between the compressed wood pieces can be maintained, wherebythe positional displacement and the like between the compressed woodpieces can be prevented.

On the other hand, in the casing structure of the compressed woodaccording to the embodiments, even if a pair of compressed wood piecesexpands or contracts, the compressed wood pieces can be kept to the samelength because the wood fiber directions in the main surface portionsare substantially symmetrical with respect to the opposing surfacebetween the compressed wood pieces, whereby the relative positionalrelation between the compressed wood pieces can be maintained.Accordingly, the positional displacement and the like between the pairof compressed wood pieces can be prevented. Further in the casingstructure of the compressed wood according to the embodiments, the woodfiber directions of the compressed wood. pieces are substantiallyparallel with the longitudinal direction of the main surface portions.Accordingly, the wood fiber directions, in which the compressed woodpieces expand and contract least, can be in coincidence with thelongitudinal direction of the casing in which the casing is mostaffected by the expansion and contraction of the compressed wood pieces,whereby the positional displacement and the like between the compressedwood pieces can be more effectively prevented. Furthermore, in thecasing structure of the compressed wood according to the embodiment, thecompressed wood pieces are also substantially symmetrical with respectto the grains, therefore the relative positional relation between thecompressed wood pieces can be more effectively maintained and a designproperty can be further enhanced. In the casing structure of thecompressed wood according to the embodiment, even if the compressed woodpiece expands and contracts, the detachable unit expands and contractsat an approximately same expansion/contraction rate with the compressedwood piece. Hence, the relative positional relation between thecompressed wood piece and the detachable unit can be maintained.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A casing structure of compressed wood that holds a predeterminedobject between a plurality of compressed wood pieces, wherein each ofthe compressed wood pieces has a main surface portion and side surfaceportions formed integrally around entire peripheral edges of the mainsurface portion and non-parallel with the main surface portion, and woodfiber directions in the main surface portions of the compressed woodpieces are substantially symmetrical with respect to an opposing surfacebetween the compressed wood pieces.
 2. A casing structure of compressedwood that holds a predetermined object between a pair of compressed woodpieces, wherein each of the compressed wood pieces has a main surfaceportion formed in a substantially square shape and side surface portionsformed integrally around four peripheral edges of the main surfaceportion and non-parallel with the main surface portion, and wood fiberdirections in the main surface portions of the pair of compressed woodpieces are substantially symmetrical with respect to an opposing surfacebetween the pair of compressed wood pieces.
 3. The casing structure ofcompressed wood according to claim 1, wherein the wood fiber directionsin the main surface portions are substantially parallel withlongitudinal directions of the main surface portions.
 4. The casingstructure of compressed wood according to claim 1, wherein grains of themain surface portions are substantially symmetrical with respect to theopposing surface between the compressed wood pieces.
 5. The casingstructure of compressed wood according to claim 1, wherein a part of acompressed wood piece is formed as a detachable unit detachably mountedon the compressed wood piece, and the wood fiber direction of thedetachable unit is substantially in coincidence with the wood fiberdirection of the compressed wood piece on which the detachable unit ismounted.